An electric motor may be described as generally comprising a stator and a rotor. The stator is fixed in position and the rotor moves relative to the stator. In AC or axial motors, the stator is typically the current carrying component of the motor generating a magnetic field to interact with the rotor. The rotor in an AC or axial motor may comprise a squirrel cage or a magnetic rotor. The field generated by the stator will propel or rotate the rotor via a magnetic field relative to the stator.
The operation of an electric motor generates heat in the form of current/resistance I2R losses, iron losses, stray losses and mechanical losses in the rotor and stator. The stator and rotor are cooled to avoid overheating which would result in demagnetization of magnets in the motor or melting or burning of other parts of the motor. Heat dissipation is the limiting factor in motor sizing and power ratings. The motor current is directly related to power output, as well as the heat generated by the motor. In electric motor applications where space is a premium such as in electric and hybrid vehicles, motors with a relatively small footprint and high power ratings are desired.
There exist a variety of electric propulsion or drive technologies used to power vehicles. The technologies include electric traction motors such as DC motors, AC induction motors, switched reluctance motors, synchronous reluctance motors, brushless DC motors and corresponding power electronics for controlling the motors. In the prior art, it has been common to couple the traction motor(s) to the front or rear wheels of the vehicle using a mechanical drive-line with reduction gears and a differential. Sometimes, the motors are mounted in the driving wheels without a differential and coupled to the wheels through speed reduction gears.
While such systems are functional, they suffer from higher weight, lower reliability and lower efficiency due to the mechanical drive-line (gears, differentials, transmissions, etc.) between the motor(s) and the wheels. It is desirable that heat be removed as efficiently as possible and that the weight of the motor be minimized. The more efficient the removal of heat the smaller the footprint of a motor for a specific power rating. Further, it is desirable to provide such motors having a form suitable for inclusion directly in or adjacent to a vehicle wheel. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.